1. Field of the Invention
The present invention relates generally to devices for controlling the flow of effluent from a naturally or freely depleting oil well, and more particularly, to a device for stopping the flow of effluent from a blown-out or otherwise uncontrolled oil well by freezing a plug of effluent within the well.
2. Description of the Prior Art
Oil wells are drilled into oil bearing formations which often exert tremendous pressure upon the oil, gas, and other components of effluent that escape from the formation. For example, down hole pressures within an oil well are normally relatively high, and may exceed 20,000 pounds per square inch. If this pressure is unchecked, a blow-out will occur, and oil, gas and other matter will flow uncontrollably from the well. Blow-outs may occur either during drilling operations or during production operations.
During drilling operations, mud is typically pumped into the well to counteract pressures exerted by formations into which the well extends. As used herein, the term "mud" designates a drilling fluid containing a chemically complex series of compounds used to aid the drilling process. Prior to reaching high-pressure formations, weak formations are usually encountered during the course of drilling the well. These weaker formations will crater and ultimately be destroyed if exposed to the pressure exerted by very dense or heavy weight mud. Accordingly, it is desirable to use relatively lightweight mud when drilling through such weak formations until a protective casing string is installed within the wellbore. Following installation of the casing string, heavier weight mud can be pumped into the well for controlling high pressures exerted by formations located at greater depths. However, if formation pressures encountered within the well become much larger than were initially anticipated or accounted for at a given depth, the formation pressure pushes the insufficiently-dense mud out of the well, and a blow-out results. In some cases, the formation pressure is so unexpectedly large that the drill string used to drill the well is itself pushed out of the well.
During production operations on completed wells, a blow-out condition can result if damage occurs to the well head or Christmas tree assembly which normally controls pressures exerted within the well. In the case of off-shore oil wells, such damage is typically caused by collisions with ships or by violent weather conditions. Blow-out conditions have also been known to occur during the work-over of a well, i.e., during the time that production operations are temporarily halted to allow repair, replacement, or cleaning of valves, tubing, and other equipment associated with the well.
Regaining control of a high-pressure oil well which has blown-out or suffered surface damage is a time-consuming and hazardous operation, particularly for oil wells located off-shore. The uncontrolled flow of oil from the well results in severe pollution and waste problems, and the area near the well head may become engulfed in flames. Thus, oil well blow-outs can cause astronomical financial losses and major environmental problems. Furthermore, attempts to regain control of such blown-out oil wells can result in severe injuries or deaths.
At present, efficient oil well disaster control principally relies upon prevention of blow-outs. Devices known as blow-out preventers are typically used during drilling operations for controlling unexpected pressures within the well. Blow-out preventers have generally been successful in preventing blow-out conditions during drilling operations. However, blow-outs still occur during drilling operations by exceeding design limits, or by improper operation or malfunction of the blow-out preventer. Devices known as down hole storm chokes are typically utilized in conjunction with producing oil wells. However, down hole storm chokes are continually exposed to an abrasive, high temperature environment. Therefore these storm choke devices are soon degraded by their operating environment and frequently malfunction.
One method of controlling a blown-out oil well is disclosed in U.S. Pat. No. 3,738,424. The patent disclosure is particularly directed to controlling blow-outs in off-shore, producing oil wells. Following installation of the intermediate casing within the well, valves are welded to the external surface of the outermost casing by divers who perform the welding operations under water. Each valve receives a drill bit for drilling a hole through the various layers of casing in the event of a blow-out after production operations have commenced. After a hole has been drilled through the layers of casing proximate to each valve, the drill bits are removed from the valves, and tubes for circulating liquid nitrogen are connected to the valves. The liquid nitrogen is circulated adjacent the production tubing string for freezing a solid plug therein.
The method for controlling blown-out oil wells disclosed in the above mentioned U.S. patent has several disadvantageous limitations. The method disclosed therein is limited to controlling the well at a point located above the surface of the ground or ocean floor into which the well extends since it is not apparent how the various assortment of valves, drill bits, and tubing can otherwise be attached to the well and manipulated in the event of a blow-out. The need for divers to install the necessary equipment and to manipulate the equipment in close proximity to the hazardous area resulting from the blow-out is also a disadvantage. Furthermore, the method of controlling a blow-out disclosed by the above mentioned patent is operative only to freeze a plug within the production tubing string; it may not be used to control a blow-out that occurs during drilling operations. Also, the above described method is not effective to freeze a plug of effluent in the event of a packer blow-out. A packer blow-out can occur upon failure of the packer installed in a producing well to seal the annulus between the production casing string and the production tubing string above the oil producing zone. When a packer blow-out occurs, effluent flows uncontrollably out of the well through the production casing string external from the production tubing string.
Accordingly, it is an object of the present invention to provide a down hole shut-in device which can be easily installed within an oil well below the surface of the ground or ocean floor for stopping the flow of effluent from a blown-out oil well.
It is another object of the present invention to provide a shut-in device which can be used either during drilling operations or during production operations for stopping the flow of effluent from a blown-out oil well.
It is a further object of the present invention to provide a shut-in device for stopping the flow of effluent from a blown-out oil well, which device may be integrated into a convenitonal oil well casing string or tubing string.
It is yet a further object of the present invention to provide a shut-in device for stopping the flow of effluent from a blown-out or otherwise uncontrolled well wherein no mechanically deployed elements or mechanically actuated seals, of the type utilized in present oil well control devices, are required in order that the downhole shut-in device be relatively immune from abrasive wear.
It is a still further object of the present invention to provide a shut-in device for stopping the flow of effluent from a blown-out oil well located off-shore wherein divers and other personnel are not required to work in close proximity to the oil well in order to actuate the shut-in device.
It is another object of the present invention to provide a shut-in device for forming a frozen plug of effluent within the affected casing string of an oil well during drilling operations when a blow-out occurs.
It is still another object of the present invention to provide a shut-in device for forming a frozen plug of effluent within the annulus formed between the production casing string and the production tubing string in a completed, producing oil well when a blow-out occurs.
It is a further object of the present invention to provide a shut-in device for quickly and reliably forming a frozen plug of effluent within the production tubing string of a completed, producing oil well when a blow-out condition occurs.
It is a still further object of the present invention to provide a shut-in device for stopping the flow of effluent from a blown-out oil well, which device does not interfere with the passage of drilling equipment, fishing tools, instrument probes, or other oil well tools inserted into the well.
Another object of the present invention is to provide a shut-in device for stopping the flow of effluent from a blown-out oil well wherein no substantial changes in oil well drilling procedures or tooling are required.
Still another object of the present invention is to provide a shut-in device which may be remotely activated for effecting a total stoppage of effluent from a blown-out oil well.
A still further object of the present invention is to provide a shut-in device for stopping the flow of effluent from a blown-out oil well wherein activation of the shut-in device does not impede subsequent resumption of drilling or production operations after control of the oil well has been regained.